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Trying not to be distracted by a phone is, itself, distracting.

If the project you’re working on needs and deserves your full attention, put your phone away. No, really. Not just face down. Not just in a bag or a pocket. Get up, set the phone down in a different room—on silent, or maybe even just turn the thing off—and return to your desk, secure in the knowledge that your limited cognitive capacity just grew a little bit.

It’s well established that multitasking while using a smartphone drains energy and decreases performance. But new research shows that you don’t even have to interact with the phone for it to steal from your attention and cognitive abilities.

Researchers at the University of Texas-Austin gave more than 800 research subjects one of three instructions:

Leave all belongings in a separate room before proceeding to the experiment.

Place their phones face down on the desk in the testing room during the task.

Leave their phone in the place they’d normally carry it, such as a pocket or purse (which accompanied them to the testing room).

All were instructed to turn their phones to silent, with no ring or vibration. They were then given a set of tests designed to measure cognitive performance.

Those who left their phones in a separate room performed far better on all exercises than those whose devices were within arm’s reach. The effect was more pronounced on participants who rated themselves as being highly dependent on their phones.

What’s going on here, researchers say, is that trying not to be distracted by a phone is, itself, distracting. The more automatic the process of checking our phones and interacting with devices becomes, the more resources it takes to divert our focus away from those devices.

This isn’t a conscious process. When asked to rate how often they thought about their phones during the experiment, most subjects said “not at all.” Three-quarters said the phone’s location had no affect on their performance. Yet the farther a respondent was from their phone, the better he or she performed.

The paper adds to a growing body of research examining the consequences of our increasingly intimate relationship with technology. Studies have found that the mere presence of a smartphone on a table during a conversation makes people perceive it as a lower-quality discussion. The scourge of driving while texting is, in part, attributed to the fact that smartphone use has become so automatic for many of us that we don’t realize we’re doing it. The next time you automatically check your phone, remember: you don’t know what you’re giving up to do it.